In general, a refrigerator prevents deterioration and reduction of freshness of foods, by generating cool air by exchanging heat with cold refrigerants passing through a refrigeration cycle, and freezing or maintaining the foods at a low temperature by circulating the cool air in a freezing chamber and a refrigerating chamber. Therefore, the refrigerator stores various kinds of foods for an extended period of time.
Normally, the refrigerators are classified into direct cooling type refrigerators and indirect cooling type refrigerators. In the direct cooling type refrigerator, evaporators are installed on inner walls of a freezing chamber and a refrigerating chamber, and cool air generated at the adjacent parts to the evaporators in the freezing chamber and the refrigerating chamber is naturally convected to cool the freezing chamber and the refrigerating chamber. Conversely, in the indirect cooling type refrigerator, an evaporator is installed on an inner wall of a freezing chamber, a fan is installed on a cool air circulation passage, and cool air generated on the cool air circulation passage on which the evaporator has been installed is forcibly blown by the fan to cool the freezing chamber and the refrigerating chamber.
Moisture generated from foods stored in the refrigerator inside or moisture of the open air sucked into the refrigerator inside due to opening of doors generates frost on the surfaces of the evaporators. The frost formed on the surfaces of the evaporators reduces heat exchange efficiency between the air inside the refrigerator and the evaporators. A temperature deviation seriously increases in each position of the refrigerating chamber having a relatively higher temperature than the freezing chamber. Therefore, a defrost operation is essential in the refrigerating chamber.
The compressor is stopped for a predetermined standstill time to defrost the conventional direct cooling type refrigerator. As the using time of the refrigerator increases, the frost formed in the refrigerator inside is grown to cover the whole surface of the refrigerator inside. Accordingly, the user must manually defrost the refrigerator.
In addition, a defrosting heater mounted at the lower portion of the evaporator is operated to defrost the conventional indirect cooling type refrigerator, thereby rapidly performing the defrost operation. However, the defrosting heater increases manufacturing and production expenses and power consumption. Also, the defrosting heater sharply increases a temperature of the adjacent parts. As a result, the refrigerator inside temperatures are not uniformly maintained, and cooling performance is deteriorated.